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In our online poll to find out what Plus readers would most like to know about the Universe you told us that you'd like to find out if time travel is allowed. We took the question to Kip Thorne, Feynmann Professor of Theoretical Physics, Emeritus, at the California Institute of Technology, and here is his answer.

4 Comments:

I know a little GR; but no Quantum Gravity and very little QM.
I interpret the article as saying that the consensus is: Quantum Gravity can not be fit into Godel's time-closed solution to GR. Is that correct? In that case the global topology would constrain the deeper theories. Put another way Quantum Mechanics can not be embedded/formulated on an arbitrary manifold.
These are questions; not statements.
Ray

I read references 2,3
3 is quite readable.
2 is tougher and I am not through.
The idea that some local properties can't be extended globally in some topologies is not as strange as it might seem at first glance; there are other examples.
I do have doubts about some of the reasoning; but that doesn't fault the reasoning just the presumptions.
I think its possible that the "energy conditions" are not the right analysis tool. Something along the lines of Entropy (Maxwell's daemon ) might be sharper in the mathematical sense.
Ray

Th relation to Casimir vacuums was fascinating. So is the solidarity of Hawking's argument.
Although the possibilities of time travel would lead to the age old grandfather paradox, and I am not sure as to what would be a right explanation. Maybe the Copenhagen interpretation of splitting states to maintain Quantum decoherence.
Cannot say anything conclusively.

Professor risk

Are you a committed non-smoker who loves rock climbing? Then, like most of us, your have an ambivalent attitude to risk. Some risks are so much fun they're worth taking, and others you definitely stay clear of. But what's the attitude of a risk professional like David Spiegelhalter, Cambridge Professor of Public Understanding of Risk (and regular contributor to
Plus)? Find out in this short video posted on the Cambridge Ideas website.

0 Comments:

Infectious diseases hardly ever disappear from the headlines. If it's not the disease itself that hits the news, then it's the vaccines with their potential side effects. It can be hard to tell the difference between scare mongering and responsible reporting, because media coverage rarely provides a look behind the scenes. How do scientists reach the conclusions they do? How do they predict
how a particular disease will spread, and whether it is likely to mutate into a more dangerous strand? And how do they assess the impact of an intervention like vaccination, and make sure that a vaccine is safe?

Two answer these questions, we have put together a package of five articles, a podcast, and a classroom activity.

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Vaccination is an emotive business. The furore around the MMR vaccine and autism has shown that vaccination health scares can cause considerable damage: stop vaccinating, and epidemics are sure to follow. But how do scientists decide whether a vaccine and a vaccination strategy are effective and safe? We talk to Paddy Farrington, Professor of Statistics at the Open University. You can also
read the accompanying article.

0 Comments:

An amateur fractal programmer has discovered a new 3D version of the Mandelbrot set. Daniel White's new creation is based on similar mathematics as the original 2D Mandelbrot set, but its infinite intricacy extends into all three dimensions, revealing fractal worlds of amazing complexity and beauty at every level of magnification.

6 Comments:

Those interested in more about the Mandelbulb and the search for the "true 3D" Mandelbrot including an almost complete history of the last couple of years search may wish to look here http://www.fractalforums.com/

However, I'm wondering if there isn't a typo in the formula given. If it is a direct generalization of complex multiplication using Euler angles, the z-component should be:
-sin(n phi)
and not:
-sin(n theta)
Am I wrong?

LHC set for restart

After over a year of repair works the Large Hadron Collider at CERN may be restarted within the next few days. Scientists will gently prod the giant particle collider back into action, starting by circulating beams of protons at low energies and generating low energy collisions, before slowly firing it up to its full power. It is hoped that eventually
the high energy collisions will generate conditions similar to those right after the Big Bang and shed light on some of the biggest mysteries of the Universe.

To remind yourself of what the LHC is all about, read the Plus articles: